This invention relates to print heads for the magnetographic printing of images and, more particularly, to a print head constructed of crossed arrays of elongated magnetizable bars wherein individual picture elements, or pixels are formed on a magnetic medium at the intersections of the bars of the two arrays, the particular pixels being addressed by selective magnetization of bars in each of the arrays. This construction of the print head reduces complexity and cost while retaining high resolution.
Magnetrographic printing systems employ a print head, a magnetizable medium, and a toner for producing an image on a sheet of paper or other hard copy material. The magnetic medium may be carried upon a drum or upon a tape. Typically, the magnetic medium is coated upon the drum or the tape. A common form of print head comprises an array of magnet cores which are interlaced with a set of electric conductors. The magnetic cores, in cooperation with the electric conductors, form electromagnets which are selectively energizable by application of electric currents to selected ones of the electric conductors.
The print head is positioned alongside of the surface of the magnetic medium to allow each of the electromagnets to impart a magnetic field to the medium in a region directly beneath the terminus, or print-element portion, of a magnetic core, thereby to write a mark upon the magnetic medium. Energization of various ones of the electromagnets results in the formation of a set of marks on the magnetic medium, which set of marks constitute an image written on the medium by the print head. The material of the magnetic medium has sufficient coercivity so as to retain a state of magnetization until a magnetic field applied by print elements of the print head attains sufficient strength to alter the state of magnetization. Thereby, the region of a pixel is left blank or is imprinted only when a sufficient magnetic field is developed by the currents flowing in the electric conductors. The magnetic image is rendered visible by toning with magnetic ink, which ink is attracted by the local magnetic fields of the magnetically written regions. The toner is then transferred to the paper to produce the image on the paper.
In many printing applications, it is desirable to produce a high-resolution image. By way of example, such high-resolution imaging is required in the printing of small detailed characters, such as a 9-point text. A further example is the case of the printing of a picture wherein fine detail is to be rendered. In order to accomplish fine-resolution printing rapidly, it is desirable to construct a print head having an array of many closely spaced small print elements, the size of the print elements being commensurate with the smallest detail to be rendered.
A problem arises in that the construction of a print head of closely-spaced high-resolution print elements. Heretofore, both the print elements and their corresponding electrical activation conductors had to be constructed using expensive high-resolution processing technology, and since the conductors have to be electrically continuous over relatively long distances, this high-resolution processing had to be done over a large area. These considerations have made large, page-wide, high-resolution print heads unduly complex and, consequently, expensive to produce.